Send up one mate bagging IT (7)
I believe the answer is:
imitate
'send up' is the definition.
(thesaurus)
'one mate bagging it' is the wordplay.
'one' becomes 'i' (Roman numeral).
'bagging' indicates putting letters inside (bag can mean to take or obtain).
'mate' placed around 'it' is 'mitate'.
'i'+'mitate'='IMITATE'
(Other definitions for imitate that I've seen before include "Fake" , "Follow suit" , "Copy someone" , "Copy (mannerisms)" , "Reproduce" .)